Million Mile Duramax Engine Rebuild

The Perfect Diesel Engine For Towing

Some diesel enthusiasts still think of General Motors’ Duramax engine as the new kid on the block. Although, the truth is, its core architecture has now been in production longer than any of the Ford Power Strokes. And fortunately for performance enthusiasts, GM didn’t change injection systems every four years (like the 5.9L Cummins did during its first 10 years), so the aftermarket has been able to build on its knowledge base—not start over from scratch every few model years.

Yet, with all the success these 6.6L, common-rail-injected, aluminum-headed engines have had, many of them are now showing signs of wear after a decade of being in service. We’re now beginning to see way-out-of-warranty LB7 Duramax engines—which were once ahead of their time—becoming victims of time. And many of them are in need of a rebuild.

SoCal Diesel polished each of the Duramax’s crankshaft journals. They were then measured in the same spot relative to each other, and then 90 degrees from that spot to check for roundness. Since crankshaft bearings aren’t perfectly round, the measurements were taken with a dial bore gauge perpendicular to the way the engine sits in the truck. Both the flywheel and harmonic balancer were installed on the crankshaft before being spun on the balancing machine pictured here—because the Duramax engine is externally balanced. Then the bottom end rotating assembly was taken apart and reassembled in the same position when the engine was built. It’s possible to have the crankshaft internally balanced by SoCal Diesel, but we didn’t need that performance option.

SoCal Diesel polished each of the Duramax’s crankshaft journals. They were then measured i

Duramax Reborn
If you’re part of the GM diesel community and have an older Duramax that just died (or is on its way), pay attention to these steps and your aging diesel will be resurrected as the perfect engine for towing. Thanks to the fact that SoCal Diesel, one of the premiere Duramax diesel engine builders in the country, is located right in our own backyard, Diesel Power is able to bring you an exacting engine build that consists of attaining super-accurate tolerances and obliterating weak links. Though we usually think of SoCal Diesel as a performance shop first—many of the same things that work on race day will also help your truck race to the finish at the end of a long workday.

The Truck, The Carnage, The Cure
The Duramax engine we’re featuring in these pages came out of an ’03 Chevy Silverado 3500 dualie with a ZF6 six-speed manual transmission, four-wheel drive, and 130,000 miles on the odometer when it blew up towing a load of steel over the Rockies. About eight years before that fatal towing trip, the truck was fitted with a programmer, 4-inch exhaust, and an exhaust brake.

The truck spent most of its life towing off-road vehicles around the West, and as the miles added up, the truck showed the normal signs of wear and tear. The part that wasn’t normal, however, was that the ZF6 six-speed’s case broke in half at 47,000 miles, the injectors began leaking, causing one of the pistons to split. The cause of our Duramax’s death was determined to be a worn injector that was left in service too long. The leaking injector dripped fuel into the cylinder, causing that piston to be super heated, and ultimately fail when it seized in the cylinder bore. This is a very common (and preventable) problem that is made worse when the engine idles a lot, as it tends to in cold climates. Extended idling times with a bad injector is like eating fast food every day with a heart condition.

Block Preparation
After our Duramax got an autopsy and was disassembled, SoCal Diesel’s Guy Tripp discovered the main engine parts (the block, crankshaft, connecting rods, and heads) were all OK. The LB7 was then taken to SoCal’s state-of-the-art machine shop, where the block got its steel freeze plugs removed. Then it was baked and shot-peened. Once cleaned, the block was line-honed and then decked and bored 0.020-over on an RMC v30 block CNC machine to ensure the cylinders were square with the block.

But the real magic came with the finish honing of the cylinder walls. Using a Sunnen SV-10 hone and an eight-stone diamond hone (equipment typically used only for NHRA Pro Stock drag racing engines), the Duramax was blueprinted to specifications that Dmax LTD in Ohio would be envious of. Finally, the cam bearings, oil plugs, and freeze plugs were reinstalled, and the block was shot with SoCal Diesel’s traditional blue paint.

Protectors were placed on the sharp hard edges of the ARP main studs before the crankshaft was placed on half of the Clevite-assembly-lubed main bearings. SoCal Diesel specs an LB7 crankshaft whenever possible, because it has more internal counterweights and needs less external weight compared to later-model Duramax engines.

Protectors were placed on the sharp hard edges of the ARP main studs before the crankshaft

SoCal Diesel engine assembler Chris Hicks used a dial indicator with an electromagnet base to check the crankshaft endplay. This measurement is dependent on the thrust surfaces of the crankshaft compared to the side bearing surfaces. Sanding the bearing on a flat granite surface, ordering oversized bearings, or replacing or machining the crankshaft, adjusts the endplay. Also notice the two keys added to the crankshaft (arrow).

The bearing caps were secured with ARP main studs torqued to 225 ft-lb on the top and 90 ft-lb on the side.

The bearing caps were secured with ARP main studs torqued to 225 ft-lb on the top and 90 f

SoCal Diesel fit this engine with the stronger LBZ connecting rods; they have a dimple in the center (arrow). They’re thought to be good for about 50 to 100 hp more than LB7 rods.

SoCal Diesel fit this engine with the stronger LBZ connecting rods; they have a dimple in

The steel (not cast) top ring was given extra clearance (0.017 versus 0.012 inch) to ensure piston-to-cylinder wall scuffing does not occur during heavy use.

The steel (not cast) top ring was given extra clearance (0.017 versus 0.012 inch) to ensur

The new Mahle pistons were then secured to the LBZ connecting rods. SoCal Diesel also provided new full floating wristpins, wristpin clips, connecting rod bearings, and piston rings. Here is a sleeve-type spring compressor used for keeping the rings in the piston grooves while they slide into the block.

The new Mahle pistons were then secured to the LBZ connecting rods. SoCal Diesel also prov

The Mahle OEM replacement cast-aluminum piston tops have a thermal coating applied to them. The piston skirts (or sides) have a dry film lubricant to reduce friction. Hicks used a dead-blow hammer and a different style piston ring compressor to mate the two halves of the connecting rods (with bearings) around the crankshaft.

The Mahle OEM replacement cast-aluminum piston tops have a thermal coating applied to them

ARP’s new connecting rod bolts were torqued to 90 ft-lb. The connecting rod side clearance was also checked.

ARP’s new connecting rod bolts were torqued to 90 ft-lb. The connecting rod side clearance

The stock camshaft received a larger key (arrow). The more robust key prevents the cam gear from breaking free from the camshaft.

The stock camshaft received a larger key (arrow). The more robust key prevents the cam gea

This thrust plate secures the camshaft inside the block and was bolted on.

A dial indicator was used to measure the backlash between the crankshaft and camshaft gears. If this number was not within specification, the camshaft gear would have to be lapped. Next, a measurement was taken from the middle fastener holding the camshaft gear in place. This was checked to make sure the rear cam plug was in at the right depth. SoCal Diesel sets its camshaft endplay at 0.004 inch. If this installation is not done properly, the gear will rub the retaining plate.

A dial indicator was used to measure the backlash between the crankshaft and camshaft gear

The oil pump went on next. In most cases, it is checked for flatness and reinstalled. Next, the oil pump gear and reluctor wheel slides on. A reluctor wheel is also located on the camshaft, and they both send position signals to the computer.

The oil pump went on next. In most cases, it is checked for flatness and reinstalled. Next

With the number 1 piston at top dead center (TDC), the camshaft was degreed. This process checks the position of the camshaft relative to the crankshaft. It’s a quality control measure that makes sure the lobes on the camshaft operate on the valves in accordance with what’s written on the box. This is the first step with the fixture-locating TDC.

With the number 1 piston at top dead center (TDC), the camshaft was degreed. This process

The aluminum cylinder heads did not receive a porting job. They did get cleaned, checked for cracks, and had the flat surfaces resurfaced. New valve guides, seals, and a valve job were also part of the rebuild. This picture shows the dial indicator measuring valve depth.

The aluminum cylinder heads did not receive a porting job. They did get cleaned, checked f

This measuring device reveals the spring height.

Here, Hicks used a pneumatic spring compressor as the springs were added, and the retainers were installed.

Here, Hicks used a pneumatic spring compressor as the springs were added, and the retainer

The roller rockers were soaked in motor oil and then placed on top of the camshaft lobes.

A factory set of GM C-code multilayer head gaskets was placed between the resurfaced heads and block.

A factory set of GM C-code multilayer head gaskets was placed between the resurfaced heads

The head studs were torqued to 125 ft-lb.

These bridges, which allow one pushrod to operate two valves, went on next.

Valve lash was set at 0.012 inch, with the engine cold.

The stock cam was reused and checked for proper installation using the degree wheel. The LB7 Duramax uses a dual-pattern camshaft, meaning the cam actuates the intake and exhaust valves with unique lift and duration curves. On the intake side, the cam provides 0.371 inch of lift and 177 degrees of duration at 0.050 inch of lift. On the exhaust side, the cam opens the valves to 0.366 inch of lift and 184 degrees of duration at 0.050 inch of lift.

The stock cam was reused and checked for proper installation using the degree wheel. The L

A bead of silicone was applied in the channel of the front cover, rear cover, and two-piece oil pan.

A bead of silicone was applied in the channel of the front cover, rear cover, and two-piec

The front cover was added next.

Then the rear cover bolts were torqued.

Both the front and rear seals required a special tool for proper installation.

The SPX Kent-Moore part number for the rear main seal installer is J-44642 (shown); the front one is J-44645.

The SPX Kent-Moore part number for the rear main seal installer is J-44642 (shown); the fr

The aluminum part of the two-piece oil pan went on next.

The damper was installed last. The two position sensors on the left are for the crankshaft (9 o’clock) and camshaft (10 o’clock).

The damper was installed last. The two position sensors on the left are for the crankshaft

The gear on the water pump has been known to shear off the shaft in high- performance applications, so SoCal Diesel welds them together.

The gear on the water pump has been known to shear off the shaft in high- performance appl